Loud speaker and like horn



Jan- 17, 1933. F. w. LANcHEsTER 1,894,376

LOUD SPEAKERAND LIKE HORN Fi1ed-Aug. 9. 1929 FlgA.

mveN TOR Patented Jan. 17, 1933 UNITED STATES PATENT OFFICE LOUD SPEAKER AND LIKE HORN Application filed August 9, 1929, Serial No. 384,705, and

This invention relates to loud speaker and like horns and has for its object to control the distribution of sound emitted and a further object is to avoid resonance in the ampliiication horn.

The invention consists in a loud speaker horn or like horn embodying an outlet aperture of unsymmetrical form, e. g. oblong or oval, the narrower dimension being such as Will promote acoustical dillraction in planes at right angles to the longer axis and thus distribute as desired emissionin those planes, and the greater dimension is such as Will minimize acoustical diffraction and thereby concentrate the sound as desired in planes containing the longer axis.

The invention also consists in a loud speaker or like horn having lia-t sides embodying a plurality of separate elements, e. g. slats, for the purpose or purposes set forth.

The invention also consists in a loud speaker or like horn wherein said elements are mutually separated by air gaps in order to provide a predetermined amount of acoustical leakage.

The invention also consists in the method of controlling sound emission in connection With loud speaker or like horns as hereinafter described.

The invention also consists in the methods of minimizing resonance in loud speaker or like horns hereinafter described.

Referring to the accompanying diagrammatic drawing Figure l is a side elevation partly in section of a convenient construction in accordance With the present invention.

Figures 2 and 3 are plan and front views respectively corresponding to Figure l.

One mode of constructing a horn for sound reproduction apparatus in accordance With the present invention suitable for use in connection with an electrical amplication apparatus commonly termed a loud speaker is illustrated in .Figures l, 2 and 3.

According to this example a horn having a rectangular emission outlet is provided, the horn being formed of horizontal slats 2, 3 and vertical slats 4. The vertical slats 4 are extended to formi also side Walls of a boxin Great Britain August 25, 1928.

like structure housing an acoustic tube g and supporting a connecting tube and electrodynamic movement a. The vertical slats 4 of the structure are spaced apart so that small air gaps are formed between them.

In the reproduction of music in a large hall or in the open it is desirable to effect the most uniform or perfect distribution of sound of all Wave lengths laterally, that is to say in all directions at right angles to a vertical axis7 and it is to such invention more particularly applies. lVhere a horn is employed ofthe usual form the distribution of the longer Waves, i. e. notes of low pitch, may be all that is desired, but the shorter waves (and sibilants and other characteristics of speech) are emitted directionally, these sulfering less diffraction than waves of lo'sv frequency. There is consequently an observed distortion or defect in the quality of the emission according to the position occupied by the listener in relation to the horn.

This applies to some extent but less so in the case of small rooms or enclosed spaces because the reflections from the Walls reach the listener almost simultaneously with the direct sound Waves and so make up to some extent for the defect in the initial distribution.

long and short Waves alike. In explanation of this it should be realized that in the theory of Wave motion it is legitimate to regard every part of a Wave front as a source of wave emis- Thus, if the horizontal Width of the pitch) Will distribution should be over 1800 range (9()o Thus in order that adequately effected on either hand.) the usage that the present f width of the emission aperture must be made less than the wave length of highest frequency that is musically or acoustically important. Commonly this may be taken as in the region of three inches or thereabouts, but it is ordinarily unnecessary to distribute perfectly through so wide an angle and in practice it is generally found suicientto work with an aperture width of about 5 or 6 inches the narrower the angle of distribution required the wider may be the aperture according to the principles enunciated.

It is also important in large buildings to restrict the vertical distribution as far as possible. By this means roof echoes may be avoided. To this end the vertical dimension is made as great as conveniently possible so that the emergent beam of sound may be conlined to that part of the auditorium occupied by the seating accommodation or audience. Likewise in the open although there is no quest-ion of echo to be considered the vertical restriction of the beam of sound has the effect of concentrating the energy in the required direction and so increases the volume and the area effectively covered.

It will be understood from the foregoing that the form of the loud speaker emission aperture for the purpose required is the reverse of what might be thought appropriate; the lesser dimension of the emitter is that in which the widest distribution is required, and the greater dimension of the emitter is that in which concentration is advantageous.

The form of the emission aperture of the horn may be an ellipse or oval with the major axis vertical otherwise the minor axis in that direction in which good distribution is required but an oblong form is equally appropriate. c

Furthermore, the horn itself must conform in a general way to the shape of the aperture, discontinuity of section being undesirable. One result of this is that in the case of an ablong emission aperture and oblong section the sides of the horn if made integral have certain resonant periodicities and give rise to drumming when notes of corresponding frequencies are emitted. Toovercome this, and also to render the acoustical (air) column non-resonant,the sides of the horn are nconstructed of narrow planks or slats each of which, having a different natural frequency from its fellows, breaks up the resonance and minimizes acoustical distortion due to this cause. By spacing the said slats apart, i. e. allowing a narrow air gap between each slat and its neighbours, a. leakage factor is introduced into the acoustical system that effectually prevents by damping resonance due to any natural periodicity or periodicities of the air column itself.

Having now described my invention, what I claim as new and desire to secure by Letters Patents iszl. A sound-emitting horn having an elongated emission aperture, the larger dimension of which is vertical and at least four times the smaller dimension the latter being more than three inches corresponding to the wave length of a note of about 4,000 cycles per second but not more than about -siX inches coresponding to the wave length of a note of about 2,000 cycles per second.

2. A sound-emitting horn as claimed in claim l having iiat sides of considerable surftce area embodying a plurality of separate s ats.

3. A sound-emitting horn as claimed in claim 1 having dat sides of considerable surface area embodying elements mutually separated by airgaps which provide a predetermined amount of acoustic leakage.

ln testimony whereof I have signed my name to this specification. Y

i FREDERICK vlil'lLLlAllll LANCHESTER. 

